It was spring 1979, and I had just turned 15. My parents and I were living in Norfolk, where my father was the managing director of a local firm. We had an imposing but ugly house on the outskirts of town, in a road where privacy had been placed at a premium and one rarely saw, let alone knew, one's neighbour. My elder brother was estranged from the family and, having left home some years before, was now far away at college.

Life was a middle-class routine - my father worked long and hard, my mother stayed at home, trying her hand at a variety of pin-money jobs or charity work to relieve the boredom. Eventually she threw herself into local politics.

Then one day, out of the blue, my parents announced that they were moving to Nigeria. My father was taking up a post managing an electronics division of a large multinational. It was an extremely lucrative offer and would, they said, be the opportunity of a lifetime. Who knows what private deliberations went on - by the time it filtered down to me it was a fait accompli.

As we celebrated my father's good fortune, the thorny issue of what to do with me hung in the air. I was almost halfway through my O-level course and a move of schools would be disruptive. My parents were at a loss to know what to do. We had no close relatives, and my only grandparent lived miles away. I was too independent to need a nanny and I didn't want to stay with friends.

The solution came in the end from a bizarre source. In her capacity as a local councillor, my mother had befriended the chief constable of Norfolk, who suggested taking on a young police cadet who could house-share. The arrangement suited me down to the ground and seemed infinitely preferable to any of the alternatives.

That summer, I travelled with my mother to join my father in Africa for the holidays. We returned at the end of August in preparation for the new term and I was introduced to Fran, the 18-year-old I was to spend the next year with. Then, with a minimum of fuss, my mother left and returned to Africa.

She has never spoken to me about how she felt as she departed. Africa was new, colourful and exotic. She was leaving a dull market town for the post-colonial life of yacht clubs, swimming pools and a retinue of staff. But she was also leaving her young daughter.

I began this new and rather strange chapter of my life with a mixture of excited anticipation at my new-found independence and a dread of the unknown. Fran regarded me with polite indifference. She was on her own adventure, away from home for the first time. We worked out cleaning rotas and, soon enough, found ways to bump into each other as little as possible. This was made all the easier by the fact that she worked shifts and was rarely there.

Meanwhile, I was juggling the running of the household with my final year of O-levels.

My father had run through the financial side of things in some detail, but now the rest was up to me - what I ate, when I ate, when I did my homework, when I went to bed, who I saw and when I saw them. Looking back, a wilder child could have gone off the rails. But I was responsible and studious. An A-grade student and class prefect. A "coper".

Each Friday, I was allowed a lunchtime exeat from my strict school to cycle down to the bank to withdraw cash. At 15, I was not allowed a cheque guarantee or credit card, so this was my only access to money. In the evening, I would sit down in my father's study, open his desk and go through all the utility bills and my parents' credit-card statements, paying those that were due. I would then check the budget and reconcile the bank account, updating all the weekly incomings and outgoings.

On Saturday, whatever the weather, I would cycle three miles to the supermarket, purchase groceries for the week, then, precariously balancing the flimsy bags on the handlebars, would begin the slow climb home. Shopping was always stressful. A natural worrier, with a very low embarrassment threshold, I was terrified of buying more than I could pay for. I had £25 a week to spend and would frantically calculate and recalculate the running total in my head. To this day, I can do mental arithmetic at phenomenal speed.

Brought up on home cooking, it didn't occur to me to stop and I continued to prepare good food for myself. Pasta was a staple, and if friends were over, then my folder of hand-copied family recipes came out and I would rustle up schnitzel with pepper sauce (my favourite), Hungarian goulash or pork and sausage casserole. Like a little housewife, I would frantically gather papers or leftover breakfast bowls, with repeated apologies for the mess. A 15-year-old playing "house".

At weekends, I worked at the newsagent's a mile down the road, and in the evenings friends would come over, or we would meet at the pub for a few halves of underage cider. At the end of the evening, I would generally wander home alone.

Although I had boyfriends, there was no one serious and my instinct kept them at a distance. I was keenly aware of my vulnerable situation and it was in this aspect I grew up most quickly - I developed the ability to judge people and situations in a way most people don't manage until their 30s. At Christmas, my mother returned home and stumbled on the usual squalor Fran left in her wake - strewn laundry, abandoned dirty crockery and pans half-filled with week-old soup. It looked much as a student house might, with me desperately trying to keep up my mother's standards. She evicted Fran with immediate effect. "You can't leave her on her own," Fran retaliated, as she left. "It's illegal."

However, come January, my mother did return to Africa and I was left to face my mock O-levels and life by myself. School began again and my close friends now knew I was alone. They also knew it had to be a secret. I often wonder how many of their parents knew or guessed what was going on.

I don't remember feeling lonely, only frightened at times. I couldn't walk the small distance from light switch to bed in the dark, for fear of what lurked, and I would leap ridiculously from doorway to mattress. I would then superstitiously repeat prayers to a god I was convinced did not exist, to keep my parents safe. Sleep would often evade me as I was alert to every sound and would repeatedly check the locks downstairs. I immersed myself in routine to keep me safe.

Then the inevitable happened. I constantly worried about illness, as no excuse note could be produced. However, one morning as I prepared my packed lunch, I managed to drop a wooden chopping board on my foot. In agony, with what was almost certainly a broken toe, I knew I had to drag myself to school. A note was mandatory for any late attendance. Every step of the glacially paced mile to school was excruciating and, unsurprisingly, I was late. An excuse note would be needed, my form teacher insisted.

I panicked and became distraught. Alarm bells must have rung, for I then faced a barrage of questions about my domestic arrangements - who exactly was at home? With my increased distress, the teacher finally backed off and waived the excuse note.

At last, in spring 1980, I turned 16 and my parents telephoned to wish me a happy birthday and tell me Mother had hidden my present - a soft toy - under my bed when she was last in the UK. I felt a huge sense of relief. I had made it. I could, at last, legally be alone. However, in spite of my fears, my teacher never raised the subject again. I am convinced she had guessed but had decided to keep a watchful eye rather than bring in the authorities.

I went on to take my O-levels, but the sheer drudgery and hard work added to school work proved too much, and I asked to go to boarding school to take my A-levels. There, I found it hard to adjust to curtailed freedoms, but clean sheets, motherly cleaners, and a genuinely caring, supportive housemaster lifted a huge burden.

Recently, with teenage daughters of my own, I discussed the bizarre arrangement of my youth with my mother and asked her if she now felt there was anything strange in what had gone on. She didn't. She could see nothing wrong with leaving a perfectly capable child on her own. I had, after all, agreed to it, hadn't I?

My life didn't feel strange or unusual at the time. With a child's infinite capacity to adapt, I soon came to regard my situation as normal. If anything, I became disparaging of the "mollycoddled" lives I saw some of my friends living.

Today, the experience has certainly coloured my own attitudes. I am lucky to be a full-time mother to three daughters, who are inordinately messy and range from generally incompetent to woefully inept. They bask in the indulgent knowledge that they will be fetched and carried, that they will be helped with homework as needed, that a hot meal will be placed on the table every evening and that at night they can chat through problems before being tucked up and kissed goodnight.